JPH0451084A - Surface light emitting device - Google Patents

Abstract

PURPOSE:To uniform the surface brightness distribution at low cost by roughening the reverse surface of a photoconducting plate and forming a gradation layer part, which has a pattern increasing reflecting opening area with the distance from a light soruce means, between the reverse surface of the photoconducting plate and a reflecting plate. CONSTITUTION:The light from a linear light source means 3 is propagated in the photoconducting plate 2 in the face parallel direction and repeats irregular reflection by the reverse surface 2c and flank 2b of the photoconducting plate 2. Part of the reflected light which is made incident on the roughened reverse surface 2c of the photoconducting plate 2 at larger than a critical angle is reflected by a reflecting surface 8 to return to the photoconducting plate 2 and exit from the surface 2a, but the reflection quantity is adjusted by the gradation part 9 to make the reflection quanity larger at the center part (c) and small at the flank light incidence part 2b. The light bneam which is made incident on the surface above the critical angle, on the other hand, is projected from the surface and the lighr received from the surface of the photoconducting plate 2 is projectd by the diffusion surface f the diffusion plate 1 to form a face light emission part wich has a uniform, high-level brightness face distribution. Consequently, the face brightness distribution can be uniformed at low cost.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention relates to a surface emitting device used for illuminating an object to be illuminated, such as a liquid crystal display panel, from the back, and particularly relates to a surface emitting device having a thin structure. Regarding equipment.

[Prior Art] Conventionally, surface light emitting devices having built-in fluorescent tubes and the like as various linear light source means have been known. When these surface-emitting devices are used to illuminate a liquid crystal display panel or the like from the back, they must be constructed as thin as possible, and the brightness of the surface-emitting portion must be approximately uniform over the entire surface. You must do so.

The applicant of the present application has proposed an r-light diffusing device 1 in Japanese Patent Publication No. 5B-17957 that can be constructed thinly and that the brightness of surface emission is approximately equal. In other words, in this proposal, the back surface of a transparent substrate (light guide plate) with good light transmittance is subjected to directionally roughening treatment (for example, hairline processing) so that it has light reflection and transparency. Substrate (light guide plate)
A reflector is placed on the back surface of the surface, and the light source is placed on the side perpendicular to the direction of the roughening process. The luminance of the surface emitting portion is made approximately uniform over the entire surface by appropriately reflecting the light on the sloped portion.

Next, an example of the structure of a surface emitting device based on the above proposal will be described with reference to the drawings. FIG. 4 shows an example of a conventional surface emitting device called a light guide plate type side light source type. In this figure,
A pair of fluorescent tubes 3 are each arranged at the inner end of a reflective frame 4o having an oblate rectangular cross section and covered by a diffuser plate l.

A light guide plate 20 is placed between the pair of fluorescent tubes 3 that are spaced apart in this manner. This light guide plate 20 is
A side light section 20b that faces the fluorescent tube 3 and receives the emitted light from the fluorescent tube 3, a back surface section 20c whose central portion is slightly inclined as shown in the figure in order to scatter and reflect the light, It forms a surface portion 20a that emits light, and is made of an optical member that can guide light internally with low loss.

With this configuration, the light incident from the side light section 20b is guided inside and the guided light is emitted from the front surface section 20a toward the diffuser plate l. The guided light reflected at 20c is largely reflected at the central portion, and as a result, the brightness at the central portion is reduced, thereby making the brightness uniform.

Furthermore, FIG. 5 shows a light guide plate type side light source type surface light emitting device which is a further improved version of the conventional surface light emitting device. This surface emitting device is configured so that the thickness of the light guide plate 20 is tapered and becomes smaller toward the center, thereby making the luminance distribution of the diffuser plate l uniform.

On the other hand, FIG. 6 is an external view of yet another configuration of the surface emitting device, in which the light guide plate 20 is formed in a flat shape instead of providing the above-mentioned inclined portion on the light guide plate 20, and the back surface 20d is subjected to some processing. The light guide plate 20 is sandwiched between the diffuser plate l and the reflector plate 6 from above and below, and the light guide plate 20 is placed on the back surface 20d of the light guide plate 20 or on the reflective surface 6a of the reflector plate 6, approaching the center portion C shown by the broken line. A gradation pattern is directly printed in which the reflective opening area of the reflective surface 6a gradually increases as the reflective surface 6a increases, so that the amount of light from the fluorescent tube 3, which decreases at the center C, becomes uniform over the entire surface.

[Problem to be solved by the invention] However, in the conventional surface emitting device, the light guide plate 20
When providing the sloped portion 20c (Fig. 4.5), there is a problem in that an extra processing step is required to form the sloped portion on the light guide plate, which uses a material that is normally shipped flat from the factory. There was a point.

Furthermore, when printing a gradation pattern directly on the back surface 20d of the light guide plate 20 or the reflective surface 6a of the reflector plate 6, there is a problem that the overall brightness level decreases because the light conversion efficiency to the diffuser plate is poor. Ta.

Therefore, the surface light emitting device of the present invention has been made in view of the above-mentioned problems, and an object of the invention as claimed in claim 1 is to reduce the cost by not providing a sloped portion on the light guide plate, and to improve the surface luminance distribution. It is an object of the present invention to provide a surface emitting device that can make the brightness uniform and that does not reduce the brightness level.

Another object of the invention as claimed in claim 2 is to provide a surface emitting device that can further improve the brightness level in addition to the above object.

[Means for Solving the Problems] In order to solve the above-mentioned problems and achieve the objects, the surface light emitting device of the present invention has the following configuration. A surface light emitting device used in a light emitting device includes a diffuser plate that forms the surface light emitting portion on the front side by diffusing and emitting light, and a line light source means provided on the back side of the diffuser plate and on an opposing side surface. a light guide plate that transmits the light from the linear light source means inside and reflects the light on the back surface thereof, and a mirror surface provided opposite to the back surface of the light guide plate, and the light guide plate A surface light emitting device comprising: a reflector that reflects light from the back surface of the light guide plate, the back surface of the light guide plate having light reflectivity and transmittance, and having a light transmittance in the longitudinal direction of the linear light source means. A gradation layer portion is roughened with directionality so that the surface is approximately vertical, and has a pattern that temporarily increases the reflective aperture area as the distance from the light source means increases. It is formed between the reflector and the reflector.

Preferably, the gradation layer portion is made of a coating material containing a fluorescent pigment.

[Function] According to the above configuration, light from the linear light source means enters into the light guide plate through the side surface of the light guide plate. Light propagates in a plane-parallel direction within the light guide plate, and is repeatedly diffusely reflected on the back and side surfaces of the light guide plate. Of the reflected light, the light rays that are incident on the roughened back surface of the light guide plate at a critical angle or more are reflected at the reflective surface, return to the light guide plate again, and are emitted from the surface, but the amount of reflection is adjusted at the gradation part. The amount of reflection is increased at the center, and the amount of reflection is decreased at the side light areas.On the other hand, light rays that are incident on the surface at an angle greater than the critical angle are emitted from the surface and proceed to the diffuser plate. works to form a surface emitting section having a uniform and high-level brightness surface distribution by emitting light received from the surface of the light guide plate to a diffused surface.

It also works to improve brightness by being reflected in the gradation area made of fluorescent pigments.

[Examples] Preferred embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a partially cutaway cross-sectional perspective view of a surface emitting device according to an embodiment. In this figure, a diffusion plate 1 that diffuses light has light scattering performance.

For example, it is made of frosted glass. This diffuser plate 1 is a light guide plate 2
By receiving light from the diffuser plate and emitting scattered light to the outside, a surface light emitter with uniform brightness is formed. provided.

On the other hand, a transparent plastic light guide plate 2 made of an optical material with good light transmittance, such as polymethacrylic resin, is provided opposite to the back side 1b of the diffuser plate 1. Side light entrance portions 2b are formed on both sides along the longitudinal direction of the light guide plate 2, and the outer peripheral surface of the fluorescent tube 3, which is a linear light source means, is arranged close to the side light entrance portion 2b as shown in the figure. will be established. A matte finish layer may be provided on the side light entrance portion 2b at a portion corresponding to the fluorescent tube 3, thereby scattering the luminous flux emitted from the top of the fluorescent tube 3 and preventing concentration of this luminous flux. .

On the other hand, a reflective surface lla is formed on the inside of the fluorescent tube cover 11 provided so as to cover the outside of the cylindrical portion of the fluorescent tube 3, so that the output light from the fluorescent tube 3 is efficiently incident on the side surface of the light guide plate 2. After the reflection plate 8, the light guide plate 2, and the diffusion plate 1 are stacked as shown in the figure, the depth of the fluorescent tube cover 11 is adjusted so that they can be sandwiched inside the edge of the fluorescent tube cover 11. It is also possible to fix it thinly and integrally with just a few minutes.

Next, on the back surface 2c of the light guide plate 2, a hairline processing section 7 is provided in the direction connecting the pair of fluorescent tubes 3 as shown in the figure, and this hairline processing section 7 has light reflectivity and transmissivity. It will be done like this.

Further, the front surface 2a of the light guide plate 2, which faces the back surface 2c and constitutes a light emitting surface, forms a smooth transparent surface.

A reflecting plate 8 having a mirror surface 8a as a reflecting surface is provided opposite to this back surface 2C. This mirror surface 8a and the back surface 2c
A gradation layer part 9 is interposed between the dots 9, and dots 10 printed with light-blocking paint or the like are provided so as to get closer to the center C (and gradually become smaller). By providing the dots 10, the amount of light reflected on the mirror surface 8a from the above-mentioned hairline processing portion 7 is controlled, and a decrease in brightness at the center portion C is prevented.Here, this gradation layer portion 9 is Direct silk screen printing on the mirror surface part 8a of the reflection plate 8, or
Alternatively, it may be printed on the hairline processed portion 7.

Furthermore, the gradation layer portion 9 can be formed of a paint containing a fluorescent pigment, and the dots 10 of the fluorescent pigment can self-emit light to improve brightness. In this case, the pattern of the gradation layer portion 9 is slightly changed in consideration of improving the brightness of the dots 1o by self-luminescence.

Next, FIG. 2 is a plan view of the gradation layer section 9, and in this figure, the gradation (GRADATIO)
N) shows an example of the pattern, in which the dots 10 are regularly arranged in line symmetry with the center C as the center,
The diameter of the dots in the central portion C is made sufficiently smaller than the diameter of the dots near the above-mentioned side light entrance portion 2b, while the dots adjacent to each other are alternately arranged in a staggered manner.

To explain the operation of the surface emitting device described above, light from the fluorescent tube 3 enters into the light guide plate 2 via the side light entrance portion 2b of the light guide plate 2. Light propagates in the plane-parallel direction within the light guide plate 2, and is repeatedly diffusely reflected on the back surface 2c and front surface 2a of the light guide plate 2. Of the reflected light, the light that is incident on the hairline processing portion 7 of the light guide plate 2 at a critical angle or more is reflected by the mirror surface 8a, returns to the light guide plate 2 again, and is emitted from the surface 2a. As a result, the amount of reflection is made thicker at the center C, and the amount of reflection is made smaller near the side light section 2b.On the other hand, light that is incident on the surface 2a at a critical angle or more is directly emitted from the surface. , proceed to the diffuser plate 1. The diffuser plate 1 forms a surface emitting portion having a uniform and high-level luminance surface distribution by emitting the light received from the surface 2a of the light guide plate 2 from the diffuser surface.

In addition, the gradation dot 9 made of fluorescent pigment emits light by itself to improve brightness.

FIG. 3 is a relative comparison diagram of luminance distribution of surface emitting devices. In this figure, a curve W indicated by a broken line indicates the luminance distribution between the central portion C and the side light incident portion 2b of the conventional surface emitting device. Further, a curve X shown by a solid line shows the luminance distribution when the above-mentioned gradation Iza 9 is formed with a light-blocking paint, and a curve 2 shown by a dashed dotted line shows the luminance distribution when the above-mentioned gradation Iza 9 is formed by a paint containing a fluorescent pigment. This shows the case where it is formed. As is clear from these curves, the brightness distribution of the surface emitting device of this embodiment shown by curves X and Z has a smaller slope (and the brightness distribution is more uniform) than the curve W of the conventional example. Because of its high brightness level, it is particularly suitable for lighting the back of LCD panels.

As described above, according to the surface emitting device of the present invention, by using a light guide plate and arranging linear light source means on both sides of the light guide plate, it is possible to reduce brightness attenuation and obtain uniform brightness compared to the conventional method. However, the number of linear light source means is not limited to one pair, and the linear light source means may be provided only on one side of the light guide plate.

[Effects of the Invention] As detailed above, according to the surface emitting device of the present invention, since no slope is provided on the light guide plate, the cost can be reduced, and the surface luminance distribution can be made uniform, so that the luminance level does not decrease. It is possible to provide a surface-emitting device that does not require a surface emitting device.

Furthermore, it is possible to provide a surface emitting device that can further improve the brightness level.

[Brief explanation of the drawing]

Fig. 1 is a partially cutaway cross-sectional perspective view of a surface emitting device of one embodiment, Fig. 2 is a plan view of the gradation seat 9, Fig. 3 is a relative comparison diagram of the luminance distribution of the surface emitting device, Figs. FIG. 5 is an external view of a conventional surface emitting device, and FIG. 6 is an external view of yet another structure of the surface emitting device. In the figure, 1... Diffusion plate, 2... Light guide plate, 2b... Side light section, 3... Fluorescent tube, 8... Reflection plate, 8...
Mirror surface, 9... gradation seat, 10... dot, 11... fluorescent tube cover.

Claims (2)

[Claims] (1) A surface emitting device in which a surface emitting section is used in contact with or in close proximity to an object to be illuminated, comprising: a diffuser plate that forms the surface emitting section on the front side by diffusing and emitting light; and a back side of the diffuser plate. a light guide plate that is provided with a line light source means on opposing sides thereof, transmits light from the line light source means inside, and reflects the light on its back surface; A surface light emitting device comprising: a mirror surface provided as a mirror surface, and a reflecting plate that reflects light from the back surface of the light guide plate on the mirror surface, the back surface of the light guide plate having a light reflective property. and the surface is roughened in a directionality so as to have transparency and to be substantially perpendicular to the longitudinal direction of the linear light source means, and the area of the reflective opening is gradually increased as the distance from the light source means increases. A surface emitting device, characterized in that a gradation layer portion having a pattern is formed between the back surface of the light guide plate and the reflection plate. (2) The surface emitting device according to claim 1, wherein the gradation layer portion is made of a coating material containing a fluorescent pigment.